This invention relates sensors and, more particularly, to a high temperature flexural mode piezoelectric dynamic pressure sensor.
When pressure (stress) is applied to a material it creates a strain or deformation in the material. In a piezoelectric material this strain creates an electrical charge. This electrical charge can be used as proxy for a pressure being exerted on the piezoelectric material. As such, a diaphragm that is either formed of or carries a piezoelectric material may be supported by a substrate as used as a pressure sensor in certain applications. Such a sensor may be referred to as a flexural mode piezoelectric sensor herein.
Although flexural mode piezoelectric pressure sensors have been widely used. A typical configuration of such a sensor including a sensing film stack comprising a top electrode, a sensing piezoelectric layer and a lower electrode all supported on a diaphragm. The diaphragm is, in turn supported on a substrate that may include a chamber formed therein. Limited by the material's thermal, mechanical and chemical stabilities for piezoelectric layer, electrode, and substrate, and also limited by the method to integrate them as a pressure sensor, most of such traditional piezoelectric pressure sensors are for low temperature applications (T<500C). For example, in some cases, an AIN based high temperature pressure sensor structure while the operation temperature is limited by the silicon based substrate material (T<500° C.). For harsh environmental pressure sensing with high temperature (T>700C), such as in an air craft turbine, such a sensor requires the piezoelectric layer to maintain its piezoelectric property while keeping its dielectric property. Such a sensor would also need to be a piezoelectric material that is electrically, mechanically and chemically stable at high temperature. These requirements exclude most of the commonly used piezoelectric materials, substrate material and even the electrode material.